Protein adhesive composition



Patented May 6, 1952 rnorsm ADHESIVE COMPOSITION Clark 0. Heritage, Cloquet, Minn, assignor to Weyerhaeuser Timber Company, Longview, Wash, a corporation of Washington No Drawing. Application July 13, 1948, Serial No. 38,552

9 Claims. 1

This invention relates to protein adhesives, and more particularly to the improvement of said adhesives by admixture therewith of the comminuted bark of trees or selected components thereof.

Glues or adhesives of the protein type, such as glues made from soybeans, animal matter, fish substance, casein and blood are subject to considerable difiiculty in their use, due to the lack of stability of their viscosity. Proteinaceous glues tend to foam upon mechanical agitation, and the foamed condition is likewise unstable, changing rapidly with time. The instability of the foam causes the specific gravity to be constantly changing, and contributes to the instability of the viscosity. In ordinary use, the glue or adhesive is made up in accordance with specified formulations to a viscosity which enables the application of the adhesive in a layer of the desired consistency and having a composition such that a predetermined weight of adhesive is applied to a given area.

A major use of glue is in the manufacture of plywood. Glue is applied to the veneer surfaces to be joined by means of spreader rolls. The glue feeds to the rolls by gravity and the amount of glue to be applied is determined by constructing and adjusting the spreader to apply a predetermined volume calculated to correspond to a given weight of glue to be applied per thousand square feet of double glue line. Under conditions of normal mill operations, a period of time of from four to six hours may easily elapse between the time that the glue mixture is prepared and the time that the last of the mixture is applied to the surfaces to be joined. It will be obvious, under such conditions, that if the viscosity changes during this interval of time, or if at any time during the process a change occurs in the extent to which the glue is foamed, the quantity of adhesive material dispensed by the glue spreader will contain different weights of glue substance per square foot unit of surface to which it is applied. A change in viscosity during the storage life affects the amount of glue flowing by gravity to the spreader, the weight of the glue spread, and the quality of plywood made.

It is an'object of the present invention to provide, by the addition of comminuted bark, or selected botanical tissue components of bark, to the protein glue mix, the necessary stability of viscosity of the glue, thereby assuring a substantially constant ratio of weight per unit of volume of glue throughout the period of use. It has also been found that the glue, when admixed with the parenchyma tissue of bark, resultsv in the production of a bonding strength between the surfaces to be united greater than when the protein glue is used alone.

The following examples illustrate the invention. A standard soybean glue base, identified herein for convenience of reference as formulation A, consisting of 1200 grams of dry soybean glue base material, was modified by substituting a selected bark fraction for 15% of the. 1200 grams of dry glue base. In other words, the altered dry glue base consisted of 1020 grams of soybean proteinaceous material and grams of comminuted bark fraction. The dry glue base Was mixed with 2400 grams of water for approximately 7 minutes and then the other additives regularly employed in protein glue formulations, such as additional water, lime solution, caustic soda solution (NaOH), and sodium silicate, were added in sequence. It was found that when the standard glue mixture was altered by the addition of the 15% of bark material, it was necessary, in order to obtain a viscosity comparable to that of the standard formulation, to alter the proportions of the following four additive constituents in the following manner:

It will be noted that this alteration, necessitated by the thickening action of the bark, is economically advantageous in promoting the use of a larger percentage of water in theadhesive.

The marked improvement in the viscosity sta- 3 bility of the glue modified with the bark material is ably illustrated in the following graph:

foaming of the standard protein glue, improved by the use of the bark material in the formulasfdnddd A s is mdifi'ed Sta d d A m The viscosity units shown vertically at the left hand side of the graph are expressed as degrees MacMichael deflection at 40 revolutions per minute measured with a No. 22 wire suspending a small dasher in a large cup filled with glue. The units shown horizontally at the bottom of the graph indicate elapsed time in hours.

The standard glue formulation and the modified formulation were prepared at the same time and processed in the same manner. Test panels of Douglas fir, 3-ply, construction, were then prepared for concrete form grade plywood. A glue spread of 85 pounds per thousand square feet of double glue line was employed. A pressure of 200 pounds per square inch was applied at a press temperature of 260 F. for 2 minutes. The samples were tested in accordance with the tests promulgated by the Douglas Fir Plywood Association as standard for concrete form plywood, which provides that the samples shall be submerged in water at room temperature for a period of four hours, followed by drying at a temperature not to exceed 100 F. for a period of hours. This cycle shall be repeated until all samples have failed. More than two inches of delamination along the edge of a sample shall be considered as failure. It is further provided that when testing from mill-made panels, five to ten 6" x 6- panels shall be selected from one panel in a specified manner and that the average number of cycles which the five samples from one panel shall withstand is ten, or that specific panel shall be rejected. The test results were as follows:

Standard Glue Modified Glue No. of Gycles Inches De- No. of Cycles Inches De- Oompleted lamination Completed lamination Cycles Cycles 10 10 Failed 1 23 10 1 Failed 2 6 10 1 1;

It will thereby be seen that not only are the processing diffioulties, due to changing viscosity and tion, but also that an improved quality of plywood results.

The tests were repeated in connection with the production of interior grade plywood, using a slightly different soybean glue formulation identified herein for convenience as formulation B. The dry protein base material of this formulation was likewise modified by the substitution of 15% thereof by the same selected bark fraction employed in formulation A. Three 12" by 12" test panels for each test were constructed of 3-ply, Douglas fir veneer, pressed at 200 pounds per square inch and at a temperature of 280 F. for difierent intervals of time. The panels as thus prepared were tested by a two cycle test which is the standard required for interior grade soybean glues. The test results were as shown below:

Formulation B Modi- F01 mulction B fied Press time No 0f (Min.) No. of Panels Inches Dy Paliels Inches ggs 2 lamination Completing ggg i 2 Cycles lpassedflfailod... 9 on Failure. All l l 1 passed, 2 failed... 14 on Failure .do 1 5. All do The bark fraction employed in the preceding tests was a mixture obtained by a process hereinafter described which passes through a 65 mesh screen having openings of .0082 inch, and is retained on a 325 mesh screen (Tyler Ro-tap Standard) and which consists of the various components of Douglas fir bark in approximate proportions as follows, 40% parenchyma tissue, 40% fiber, and 20% cork. The fine particle size fiber tissue in this fraction constitutes relatively inert material. The parenchyma tissue and cork, however, have been found to be highly reactive to alkali, particularly the parenchyma tissue, and are, therefore, believed to be the active components in contributing the improved results'to the protein glue. For instance, relatively pure cork of Douglas fir is found to be 65% soluble in a 2% sodium hydroxide solution; the parenchyma tissue is 78% soluble; but the fiber component is only 28% soluble. Either parenchyma tissue or the finely comminuted cork of coniferous trees, or a mixture in which these components predominate, may therefore be employed with results effective in like manner to the results obtained by the use of the selected fraction employed in these experiments.

The bark products used in the formulations of the protein glues of the present invention may be obtained from the barks of many species of trees. Particularly suitable are the barks of trees used commercially as sources of lumber and wood products, since the barks of such trees are obtained in large quantities at low cost. Representative of such trees are the members of the genus Pinus, particularly the soft or white pine, the sugar pine, the Western yellow pine, the Southern yellow pine, etc.; the members of the genus Abies, particularly the white fir; the members of the genus Picea, especially the white spruce; the members of the genus Tsuga, especially the species heterophyle, commonly known as Western hemlock, and the species taxifolia of the genus Pseudotsuga. The last named, which is commonly known as the Douglas fir, is especially well suited for use as a source of the bark constituents to be used in formulating the adhesive compositions of the invention, since it contains a relatively large proportion of bark (about 15% by Weight based on the weight of the log),

and is available in large quantities from commerlarger. The particles are resilient and spongy in character; they are of low density, being partialdisclosed in the patent to Anway for Method of Treating Bark, No. 2,437,672, issued March 16, 1948, and in the copending applications of Robert D. Pauley for Production of Pure Bark Fiber,

Serial No. 623,251, filed October 19, 1945, now Patent No. 2,446,551, issued August 10, 1948, and of Bror L. Grondal and Calvin L. Dickinson for method of Treating Bark, Serial No. 572, filed January 5, 1948; said applications having a common assignee with thi application. These methods are based upon the discovery that when the whole bark is subjected to a pulverizing operation at a controlled moisture content, the nonfibrous components of phloem are relatively friable as compared with the cork and sclerenchyma tissue. The whole bark is, accordingly, subjected to one or more comminuting operations at a controlled moisture content, whereby the non-fibrous phloem is reduced to a powder, the fiber bundles are opened up to release the individual fibers, but the relatively resistant aggregates of cork cells comprising the cork layers are not substantially reduced in size. There are thus produced three fractions having different particle sizes, i. e. powdered phloem, ultimate fiber or stone cells, and natural cork. These may be separated by employing appropriate mechanical methods, such as screening, flotation, or air separation.

The cork is obtained as aggregates of cork cells in the form of flakes or granules, depending upon the treatment it has received. The size of the cork particles is such that they are mostly retained on a 28 mesh screen having openings of approximately 0.02 inch. In the case of Douglas fir, the particles may range in size to 0.5 inch or 1y filled with air; and have, in general, many of the properties customarily associated with cork.

The bark fiber obtained from Douglas fir by procedures such as those described above is obtained largely in the form of ultimate fibers which, when viewed under the microscope, are spindle shaped and vary in size, being from 0.016 inch to 0.090 inch in length, and from 0.0016 inch to 0.008 inch in thickness at the mid section, with the bulk of the fiber particles having an average length of about 0.054 inch and an average thickness of about .005 inch. Because of their elongate nature, the ultimate fiber particles may be obtained, either as overs on a 48 or 65 mesh screen, or they may .be obtained as fines from these screens, depending on the screening process. In the latter instance, the fibers are caused to pass endwise through the screen. They are hard, strong, and tough, and appear to have been but little damaged by the braying action to which the whole bark has been subjected. They are of relatively high density, being heavier than water.

In the barks of Western hemlock and Abies concolor, the sclerenchyma tissue is chiefly in the form of stone cells. The stone cells substantially all pass through a 28 mesh screen having open ings of .0232 inch, but a major portion are retained on a 65 mesh screen having mesh openings of .0082 inch. Stone cells are characterized by having diameters essentially alike, and may be roughly rounded, polyhedral, short cylindrical, or very irregular, in general the stone cells being without particular form. The walls of stone cells are very thick and strongly lignified.

A substantial portion of the larger-sized cork particles and the stone cells or fiber i removed as overs'from 65 mesh screens, and the remainder is the source of the mixture employed in the present invention. It is generally designated nonfibrous phloem and is obtained in the form of a dark-colored, usually brown, pulverulent powder, sometimes referred to as bark powder, and chiefiy comprises parenchyma tissue. As ordinarily obtained, parenchyma tissue has a particle size such that it will substantially all pass through a 65 meshscreen having mesh openings of .0082 inch in size. In fact, approximately half will pass through a 200 mesh screen and only a small percentage is retained on a mesh screen. The parenchyma tissue may be separated into smaller particle sizes by screening, particularly if first subjected to a micro-pulverizing operation. The bark powder, like the bark fiber, is heavier than water, having a density of 1.42 grams per cubic centimeter in the case of Douglas fir. For some uses it may be desirable to employ bark powder having a smaller particle size, e. g. particles sufficiently fine to pass through a 325 mesh screen. The fraction thus obtained consists of approximately 96% parenchyma tissue and constitutes an ideal source when it is desired to use relatively pure parenchyma tissue as the reactive component.

Because of the control relationship established between the particle sizes of the bark tissue coponents and the comminuting and separating procedures of the hereinbefore-referred-to bark treating processes, the various fractions of bark components identified herein are obtained in substantially uniform composition with respect to the proportions of the botanical components, regardless of the extent to which the tissue components may have varied in the natural bark.

Hence, the properties contributed by a given weight of a particular fraction of bark to the adhesive composition may be relied upon as bein fairly constant from one batch to th next. It will also be readily appreciated that in those embodiments of the invention where a particular property contributed by a particular tissue component of bark is desired, the more substantially pure the bark fraction is in terms of the particular bark component, the more advantageous will be the use of a purer component source.

While the scientific explanation of invention is not fully known, it is believed that the apparent value of the bark material in the glue formulation is to selectively absorb or react with the caustic employed in the standard protein glue formulation and thus retard the reaction of the caustic with the proteinaceous matter. The lack of stability of protein glue of standard formulation may be due to a slow reaction occurring between the caustic and the protein which is thus constantly changing the chemical composition of the material. This reaction initially tends to thicken the protein and causes a gradual breakdown of the protein which in turn destroys the adhesiveness of the glue. The comminuted bark components have a pH ranging from 3.6 to 4.0 in aqueous suspension and may, therefore, be regarded as weak acids, which function as buifers to retard the action of the caustic on the proteinaceous matter. Thus there is a preferential reaction of caustic and bark material rather than the reaction of caustic and protein which would occur if the bark material were not present.

Having thus described and explained the invention, What is claimed is:

1. An aqueous protein adhesive which maintains its original viscosity during the interval of time between its preparation and application to the object to be glued, comprising a protein glue base and a water-soluble alkaline compound of an alkali metal, said adhesive having a buffer to retard the action of said alkali on the protein glue, said buffer being furnished to the protein adhesive by having present the alkali-reactive comminuted bark material of a coniferous tree, said bark material in aqueous solution being characterized by a pH between the limits of about 3.6 and about 4, said bark material comprising principally alkali-reactive parenchyma tissue and cork.

2. The adhesive composition defined in claim 1 wherein the parenchyma tissue of the comminuted bark of the coniferous tree is present in a predominating proportion relative to the cork.

3. The adhesive composition defined in claim 1 wherein the protein glue base is a soybean glue base.

4. An aqueous protein adhesive which maintains its original viscosity during the interval of time between its preparation and application to the object to be glued, comprising a protein glue base and a water-soluble alkaline compound of an alkali metal, said adhesive having a buifer to retard the action of said alkali on the protein glue, said buffer being furnished to the protein adhesive by having present the alkalireactive comminuted bark material of a coniferous tree, said bark material in aqueous solution being characterized by a pH between the limits of about 3.6 and about 4, said bark material being principally alkali-reactive parenchyma tissue.

5. An aqueous protein adhesive which maintains its original viscosity during the interval of time between its preparation and application to the object to be glued, comprising a protein glue base and a water-soluble alkaline compound of an alkali metal, said adhesive having a buffer to retard the action of said alkali on the protein glue, said buffer being furnished to the protein adhesive by having present the alkali-reactive comminuted bark material of a coniferous tree, said bark material in aqueous solution being characterized by a pH between the limits of about 3.6 and about 4, said bark material being principally alkali-reactive cork.

6. An aqueous protein adhesive which main tains its original viscosity during the interval of time between its preparation and application to the object to be glued, comprising a protein glue base and a water-soluble alkaline compound of an alkali metal, said adhesive having a bufier to retard the action of said alkali on the protein glue, said buffer being furnished to the protein adhesive by having present the alkali-reactive comminuted bark material of a coniferous tree, said bark material in aqueous solution being characterized by a pH between the limits of about 3.6 and about 4, said bark material comprising about 40% parenchyma tissue, 40% fiber, and 20% cork.

7. An aqueous protein adhesive which maintains its original viscosity during the interval of time between its preparation and application to the object to be glued, comprising a protein glue base and a water-soluble alkaline compound of an alkali metal, said adhesive having a buffer to retard the action of said alkali on the protein glue, said buffer being furnished to the protein adhesive by having present the alkali-reactive comminuted bark material of a coniferous tree, said bark material in aqueous solution being characterized by a pH between the limits of about 3.6 and about 4, said bark material being present in the ratio of 15 parts of bark material to parts of protein base taken on the dry weight thereof.

8. An aqueous protein adhesive which maintains its original viscosity during the interval of time between its preparation and its application to the object to be glued, comprising a protein glue base and comminuted alkali-reactive bark of a Douglas fir tree in an amount to retard the action of the alkali on the protein during said time interval; said bark material comprising cork, parenchyma tissue, and fiber, the latter being 28% soluble, the cork 65% soluble, and the parenchyma tissue 78% soluble in a 2% sodium hydroxide solution.

9. An aqueous protein adhesive which maintains its original viscosity during the interval of time between its preparation and application to the object to be glued, comprising a protein glue base and a water-soluble alkaline compound of an alkali metal, said adhesive having a buffer to retard the action of said alkali on the protein glue, said bufier being furnished to the protein adhesive by having present the alkali-reactive comminuted bark material of a coniferous tree, said bark material in aqueous solution being characterized by a pH between the limits of about 3.6 and about 4.

CLARK C. HERITAGE.

(References on following page) 9 10 REFERENCES CITED Number Name Date The followin references are of record in the 21437572 Anway ar- 16 1943 file of this pat ent: 587 Goss Oct. 25, 1949 UNITED STATES PATENTS 5 OTHER R NCES Number Na Date Chem. Eng, July 1947, pgs. 159, 160, 162.

1,777,157 Biddle Sept, 30, 1 30 astics, Au ust 1947, pgs. 44, 6567. 1,87 ,329 Laucks et a1 A 9, 1932 Paint Manufacture, February 1948, pgs. 55 1,892,486 Dunham Dec, 27, 1932 and 2,290,955 Gorman July 28, 1942 1 

1. AN AQUEOUS PROTEIN ADHESIVE WHICH MAINTAINS ITS ORIGINAL VISCOSITY DURING THE INTERVAL OF TIME BETWEEN ITS PREPARATION AND APPLICATION TO THE OBJECT TO BE GLUED, COMPRISING A PROTEIN GLUE BASE AND A WATER-SOLUBLE ALKALINE COMPOUND OF AN ALKALI METAL, SAID ADHESIVE HAVING A BUFFER TO RETARD THE ACTION OF SAID ALKALI ON THE PROTEIN GLUE, SAID BUFFER BEING FURNISHED TO THE PROTEIN ADHESIVE BY HAVING PRESENT THE ALKALI-REACTIVE COMMINUTED BARK MATERIAL OF A CONIFEROUS TREE, SAID BARK MATERIAL IN AQUEOUS SOLUTION BEING CHARACTERIZED BY A PH BETWEEN THE LIMITS OF ABOUT 3.6 AND ABOUT 4, SAID BARK MATERIAL COMPRISING PRINCIPALLY ALKALI-REACTIVE PARENCHYMA TISSUE AND CORK. 